1. Field of the Invention
The present invention relates to a surface light source device, a manufacturing method of the same, and an image display device.
2. Description of Related Art
There is a surface light source device that illuminates using a light source, such as a cold cathode fluorescent lamp (CCFL) and a light emitting diode (LED). The surface light source is used, for example, as an illumination device by using the light source as direct illumination and in an image display device, such as a TV set and a personal computer, by using the light source as backlight illumination.
One type of image display device equipped with the surface light source device is a liquid crystal display using a liquid crystal panel as a display panel. The liquid crystal display is a non-self-luminous display. Accordingly, it is necessary to include a surface light source device that irradiates light to the liquid crystal panel from behind. In this case, the surface light source device is used as a backlight that irradiates light to the liquid crystal panel from behind.
The surface light source device chiefly includes a linear lamp, a reflection sheet that reflects light emitted from the lamp toward the liquid crystal panel, a diffusion member that obtains homogeneous planar light by diffusing light from the lamp and the reflection sheet, and a housing that encloses the foregoing members. For those who supply the surface light source devices into the market, it is one of the goals to achieve a size reduction of the surface light source device by reducing the number of lamps serving as light sources.
There is a method of shortening a distance between the light source and the diffusion member as a measure to achieve a size reduction of the surface light source device. However, when the distance between the light source and the diffusion member is shortened, the presence of the lamp serving as the light source is more readily acknowledged as a lamp image. The lamp image referred to herein means a phenomenon in which luminance becomes higher in a portion where the lamp is present than in the other portions when the surface light source device is viewed over the diffusion member, so that the shape of the lamp is visually confirmed. Such being the case, as a technique of reducing luminance irregularities, for example, JP-A-10-283818 proposes a technique of disposing a lens sheet between the light source and the reflection sheet. It should be noted, however, that the cited reference fails to teach a method of fixing the lens sheet.
On the other hand, a large surface light source device uses a fixing member referred to as a lamp supporter or a lamp clip in order to maintain a relative positional relation among the respective members. The fixing member is normally provided with a support portion that maintains a distance between the diffusion member and the reflection sheet, at least one lamp fixing portion used to fix the lamp, and an attachment portion used to attach the fixing portion itself to the housing. A method proposed in the related art is to fix the lens sheet and the reflection sheet at the same time using the fixing member.